There was at least one computer virus which was able to erase Flash ROM BIOS content, rendering computer systems unusable. CIH, also known as "Chernobyl Virus", appeared the first time in Mid 1998 and became active in April 1999. It affected systems BIOS and often they could not be fixed on their own since they were no longer able to boot at all. To repair this, Flash ROM IC had to be ejected from the motherboard to be reprogrammed somewhere else. Damage from CIH was possible since the Virus was specifically targetted at the then wide-spread Intel i430TX motherboard chipset, and the most common operating systems of the time were based on the Windows 9x family allowing direct hardware access to all programs.
Modern systems are not vulnerable to CIH because of a variety of chipsets being used which are incompatible with the Intel i430TX chipset, and also other Flash ROM IC types. There is also extra protection from accidental BIOS rewrites in the form of boot blocks which are protected from accidental overwrite or dual and quad BIOS equipped systems which may, in the event of a crash, use a backup BIOS. Also, all modern operating systems like Linux, Mac OS X, Windows NT-based Windows OS like Windows 2000, Windows XP and newer, do not allow direct hardware access to user mode programs. However, many Windows users run all programs in administrative mode, which allows direct hardware access. Nonetheless, as of year 2008, CIH has become almost harmless and usually just bothers users by infecting executable files without being able to cause any real harm, only triggering numerous virus alerts from antivirus software. Other BIOS viruses remain possible, however.
